Notiz über einen Zugang zu β, γ-ungesättigten Carbonsäurederivaten mit Hilfe der Amidacetal-Claisenumlagerung. Über synthetische methoden, 17. Mitteilung

Note on a preparation of β, γ-unsaturated carboxylic acid derivatives using the amide acetal Claisen rearrangement 3-(Trimethylsilyl)allyl alcohols smoothly undergo the amide acetal Claisen rearrangement furnishing allyl silanes. Subsequent protolysis with HF at ?20° provides a convenient, stereoselective method for the preparation of β, γ-unsaturated carboxylic acid derivatives. Three model examples illustrate the procedure.     

Zur Kenntnis des Faktors F430 aus methanogenen Bakterien: Struktur des proteinfreien Faktors

Factor F430 from Methanogenic Bacteria: Structure of the Protein-free Factor Factor F430, the porphinoid nickel-containing coenzyme of the methylcoenzyme-M reductase of metanogenic bacteria is shown to be the 3³,8³,12²,13³,18²-pentaacid derivative of the pentamethylester F430M, the structure of which had been determined previously (see structural formulae 1 and 2 ). The structure assignment rests on chromatographic, UV/VIS-, CD-, IR-, and ¹³C-NMR-spectroscopic as well as FAB-mass spectral comparision of F430 with F430M and the pentaacid prepared by acid-catalyzed hydrolysis of F430M. In the cells of Methanobacterium thermoautotrophicum, factor F430 is present in a ‘bound’ and also, depending on the growth conditions, in ‘free’ form, the latter being defined as the part of total F430 that can be extracted from the cells under extremely mild conditions (80% EtOH at 0–4°). From the (protein)-‘bound’ form, F430 is extracted by subsequently treating the cells at 0–4° with 80% EtOH containing (e.g.), 2m LiCi. From both sources, the extracted factor is the same pentaacid, and there is no indication for the existence of a protein-free F430 species that would contain additional (covalently bound) structural elements.     

Nitroxyl radicals and nitroxylethers beyond stabilization: radical generators for efficient polymer modification

Beyond traditional polymer stabilization, sterically hindered piperidine derivatives move into new application areas where radical functions are key elements. Recent achievements in using nitroxyl derivatives in degradation, polymerization and grafting processes are discussed together with the involved chemical reactions and the resulting material properties. The examples shown cover selected nitroxylethers (NORs) performing as flame retardants and flame retardant synergists or replacing peroxides in manufacturing controlled rheology polypropylene (PP). Furthermore, NORs and nitroxyl radicals mediate radical polymerization processes resulting in tailor-made intermediates for polymer modification via radical and condensation steps and offer access to complex polymer architecture. To cite this article: R. Pfaendner, C.R. Chimie 9 (2006).     

Axially Dissymmetric Bis(triaryl)phosphines in the Biphenyl series: Synthesis of (6,6′-dimethylbiphenyl-2,2′-diyl)bis(diphenylphosphine) (‘BIPHEMP’) and analogues,and their use in Rh(I)-catalyzed asymmetric isomerizations of N,N-diethylnerylamine

The axially dissymmetric diphosphines (?)-(R)- and (+)-(S)-(6-6′-dimethylbiphenyl-2,2′-diyl)bis(diphenyl-phosphine) ((?)-(R)- 10 and (+)-(S)- 10 ; ‘BIPHEMP’) have been synthesized, starting from (R)- and (S)-6,6′-dimethylbiphenyl-2,2′-diamine ((R)- and(S)- 16 ), respectively, via Sandmeyer reaction, liathiation, and phosphinylation. Moreover, racemic 4,4′- dimethyl- and 4,4′-bis(dimethylamino)-substituted analogues 11 and 12 respectively, and the 6,6′-bridged analogues 1,11-bis(diphenylphosphino)-5,7-dihydrodibenz[c,e]oxepin (13) were synthesized and resolved into optically pure (R)- and(S)-enantiomers via complexation with di-μ-chlorob is {(R)-2-[1-(dimethylamino)ethyl]pheny-C? N}dipalladium(II) ((R)- 18 ). The molecular structures of the diphosphines (S)- 10 and (R)- 13 and of two derived cationic Rh(I) complexes,[Rh((S)- 10 )(nbd)]BF₄ and [Rh((R)- 13 )(nbd)]BF 4 were determined by x-ray analyses. Absolute configurations were established for (+)-(S)- 10 by X-ray analyses of both the free diphosphine and of the derived Rh(I) complex, and for (?)-(R)- 13 by X-ray analysis of the derived Rh(I) complex. Configurational assignments for the substituted BIPHEMP analogues 11 12 were achieved by means of ¹H-NMR comparisons. The BIPHEMP ligand 10 and analogues 11 , 12 and 13 are the first examples of optically active bis(triaylphosphines) containing the axially dissymmetric biphenyl moiety. All these new diphosphines proved to be excellent asymmetry-inducing ligands in Rh(I)-catalyzed isomerizations of N,N-diethylnerylamine affording citronellat enamine of 98-99% ee.     

The Search for Highly Colored Organic Compounds

Until now the study of organic compounds in which the π-electron system is excited by absorbed light has been mainly concentrated on the ultraviolet and visible regions of the electromagnetic spectrum. Various new applications, such as the use of conjugated organic compounds as dye lasers or as materitals for storing information with the help of diode lasers, led to the synthesis of new compounds which absorb light in the near in infrared (NIR). It is possible to use structure-color relationships to predict the properties of such new compounds when they belong to dyestuff classes which have already been studied in detail; in this case the approach involves decreasing the energy difference between the ground state and the first excited state. A less conventional starting point is provided by molecular structures in which from the outset there is only a very small energy difference between the lowest-energy electronic states; such diradicaloid molecules occupy a special position among the various types of organic compounds. It is possible by means of suitable structural modification to stabilize such molecules in a singlet from which absorbs light at very long wavelengths (i.e. at small wave numbers).     

Polyacetylenes and Cumulenes,Potential Elements for Molecular Machines and Precursors of Carbon Clusters: A Theoretical Study

A recently described very simple procedure for estimating Hartree–Fock (H. F.) energy and accurate nonrelativistic energy has been used with simple hydrocarbons possessing C?C or C?C bonds and for the acetylene dimer. Experimental characteristics (heats of formation, ionization potentials, electron affinities), structural features, and reactivity have been discussed in terms of quantum‐chemistry characteristics at the H. F. level and also at a level including a part of electron correlation. Deviations from linearity with derivatives of long polyacetylenes and cumulenes are ascribed to the lowest‐energy deformation vibrations, which decrease rapidly when passing from short to long acetylenic and cumulenic chains. The role of derivatives and heteroanalogues of hydrocarbons under study in atmospheric and interstellar chemistry is briefly mentioned. Derivatives with enhanced stability represent potentially promising construction materials for molecular devices and also resources for the preparation of defined clusters of C‐atoms.     

Synthesis of a Sialyl Lewis x Mimic with Fixed Carboxylic Acid Group: Chemical Approach toward the Elucidation of the Bioactive Conformation of Sialyl Lewis x

The relation of the solution and bioactive conformation of sialyl Lewis x (sLe(x)) has been addressed by chemical means. To mimic the preferred solution conformation of sLe(x) 1, the more rigid analog 2 has been designed and synthesized. The sialic acid residue of 1 was replaced by a carboxylic acid function which is fixed in the equatorial position of a six membered ring acetal fused to galactose. Due to entropic considerations, an increased biological activity could be expected if the preferred solution conformation and bound form of sLe(x) were similar. Since mimic 2 was found to be inactive in an E-selectin binding assay, the bound form of sLe(x) most probably differs from the prevailing solution conformation.     

S(N)1-like reactions of bicyclic alpha-amino ethers with sulfur,nitrogen, and carbon nucleophiles. Synthesis of 1-azabicyclo[3.2.2]nonanes functionalized at carbon C2 and C6 with complete stereocontrol

[reaction: see text] In the presence of nucleophiles, Lewis acid mediated cleavage of alpha-amino ethers derived from quincorine and quincoridine affords a variety of C2-substituted and C6-vinylated 1-azabicyclo[3.2.2]nonanes. These are enantiopure and are formed in S(N)1-like reactions with complete stereocontrol. There is no leakage into 2-Nu en route to product 1-Nu or vice versa. Me(3)SiCN provides new Strecker-type alpha-amino nitriles. In the presence of TTMPP-BF(3).OEt(2), the ketene acetal Me(2)C=C(OMe)OSiMe(3) delivers enantiopure bicyclic beta-amino acid esters.     

Experimental and theoretical study of the adsorption of fumaramide [2]rotaxane on Au(111) and Ag(111) surfaces

Thin films of fumaramide [2]rotaxane, a mechanically interlocked molecule composed of a macrocycle and a thread in a "bead and thread" configuration, were prepared by vapor deposition on both Ag(111) and Au(111) substrates. X-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy were used to characterize monolayer and bulklike multilayer films. XPS determination of the relative amounts of carbon, nitrogen, and oxygen indicates that the molecule adsorbs intact. On both metal surfaces, molecules in the first adsorbed layer show an additional component in the C 1s XPS line attributed to chemisorption via amide groups. Molecular-dynamics simulation indicates that the molecule orients two of its eight phenyl rings, one from the macrocycle and one from the thread, in a parallel bonding geometry with respect to the metal surfaces, leaving three amide groups very close to the substrate. In the case of fumaramide [2]rotaxane adsorption on Au(111), the presence of certain out-of-plane phenyl ring and Au-O vibrational modes points to such bonding and a preferential molecular orientation. The theoretical and experimental results imply that the three-dimensional intermolecular configuration permits chemisorption at low coverage to be driven by interactions between the three amide functions of fumaramide [2]rotaxane and the Ag(111) or Au(111) surface.